If he is new to long range shooting, .308 is almost mandatory. Gonna be spending alot of time shooting to get good, and a .308 can put 5k-8k rounds through a barrel before it's shot out. 6.5x284 and the like tend to be barrel burners at 1-2k rounds.
.308 has some incredible factory match ammunition if you aren't into reloading yet, and so many known recipes for hand loading, you almost get to start accurate and tweak from there.
There are other factory rifles that can reach 1k out of the box (Savage 10FP, Remington 700P or 700PSS, a Remington 700 5R mil-spec, and even some standard 700 tacticals or varmints if you get a decent one). You can spend a bit more on a factory Sako TRG or Accuracy International. But this is all contrary to the question, can you do it with a Ruger...
As to whether or not a given caliber bullet can hit 1k, it's more important to ask what you want to do when you get it there. Some lower BC bullets, or underpowered ammo, might get there, but it strike the target sideways even. Hunting or "sniping" at 1k yards is a bit different than shooting paper.
That leads to the purpose of the scope. If you are benchrest shooting, yes, like the posters above said, get the thinnest reticle and highest power possible. If you are using your rig to double for hunting, you want about 1x magnification for hundred yards, so you retain some decent field of view. That means you could conceivably shoot 600 yards with a 6x scope. Most decent tactical scopes are in the 3-9x, 4-14x, 5-15x range. For weight considerations, you may want to go with a 42mm, 44mm, or 50mm objective (56-60 are usable for BR and give good light gathering, but you have to lug the gun around if its for anything other than benchrest shooting).
Also, if you are using this as an all purpose rig, you don't want to lug a 30" heavy barrel through the woods. You can get to 1k with .308 on a 20" barrel, though you do lose some bullet velocity, as compared to a 24-26" standard barrel.
The twist of the barrel also matters. A .308 can be stabilized with a 1:12 twist, though you will probably be limited to 168gr bullets (175 maybe, but dependant on each guns unique quirks).
If you haven't figured it out by now, for your first long range gun, it should be a 308. Everything is a trade-off. Carryability for velocity, wider field of view for less magnification. Long barrel life for lower BC caliber chamberings.
Some good caliber discussions and information at several sights:
http://www.6mmbr.com/index.html
http://demigodllc.com/articles/practica ... equipment/
Oh, and get ready to spend some money...